Integrated semiconductor devices are typically constructed en masse on a water of silicon or gallium arsenide. Each device generally takes the form of an integrated circuit (IC) die, which is bonded to the die-mounting paddle of a leadframe. The wire attachment pads on the die are connected with their corresponding leads on the leadframe with aluminum or gold wire during a wire bonding process. The die and leadframe are then encapsulated in a plastic or ceramic package, which is then recognizable as an IC "chip". Since nine or more leadframes are typically interconnected as a leadframe strip during the manufacturing process, a trim and form operation separates the individual chips from the strip and forms (bends) the leads of the chip into the required configuration. IC chips come in a variety of forms such as dynamic random access memory (DRAM) chips, static random access memory (SRAM) chips, read only memory (ROM) chips, gate arrays, and so forth. The chips are interconnected in myriad combinations on printed circuit boards, along with other types of discrete components such as resistors and capacitors, by any number of techniques, such as socketing and soldering.
An example of a typical leadframe strip is depicted in FIG. 1. From the point in the manufacturing process where the paddles 11 of a leadframe strip are coated with adhesive prior to die bonding until the point where the individual chips are separated from the leadframe strip rails 12 during a trim and form process, a leadframe strip is treated as a unit in the manufacturing process. Automatic handling machinery is designed to retrieve the partially complete leadframe strip assemblies from leadframe storage devices commonly called carriers. A typical leadframe strip carrier is depicted in FIG. 2. The interior of the carrier has a pair of opposed mirror-image grooved faces. Each groove on one face and its mirror-image groove on the opposing face acts as a slot into which a single lead frame strip may be inserted. The carrier of FIG. 2 is capable of supporting twenty-seven leadframe strips. The current generation of leadframe strip carriers suffers from two drawbacks: high cost of manufacture and inconvenient design.
It is not uncommon for leadframe strip carriers to cost in excess of $250 per unit. This cost is especially significant considering that a semiconductor manufacturer may need several thousand carriers of various sizes, and than since the carriers are subject to damage and wear during the semiconductor manufacturing process, they are not expected to last much more than a single year. The high cost of leadframe strip carriers is primarily due to the fact that they are invariably manufactured from aluminum extrusions. The manufacturing process requires that each carrier begin as a cut section of extrusion. Then, both ends of each leadframe strip slot must be relieved, both horizontally and vertically, to facilitate introduction of leadframe strips into the slots by mechanical leadframe strip-handling equipment. Finally, an end cap retaining groove must be machined on each side near one end of the carrier. The open end having the grooves can be closed with a cap, the cupped edges of which mate with the grooves.
Since leadframe strips come in any number of widths, a different extrusion must be used for each size of carrier. Typically, carriers having different internal width dimensions also have different external width dimensions. Such a situation complicates production machinery setup as carrier elevators, carrier holders and carrier transport machinery must be adjusted whenever the width of a leadframe strip changes.
It would be highly desirable to design a series of leadframe strip carriers, of which any individual member would have external dimensions identical to any other member of the series, and could be produced for substantially less cost than a carrier produced from an aluminum extrusion.